Henry Ford called the Model T "the universal car" because it was low-cost, easily maintained, and could successfully travel the roads of the time. Because it was the first low-priced, mass-produced automobile with standard, interchangeable parts, Model T quickly became every man's car. By October 1911 Ford opened an assembly plant in Manchester, England, its first outside North America, and by the end of 1913 had signed contracts to sell the Model T in China, Indonesia, Siam, Dutch East Indies, and Brazil.
The all new Ford Focus, like the Model T, is one of the most significant global platforms Ford has ever launched. First manufactured and introduced in Europe, this summer Ford began North American Focus production for its 2000-model-year introduction. In all, Focus will be sold in 60 different countries, according to President of Ford Division Jim O'Connor.
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In engineering the first vehicle of the Ford 2000 program, the Focus team had at its disposal all of Ford's worldwide resources. The goal: design a global platform that's easily modified to suit local markets. "Focus is one of the most intensive, CAE-driven programs Ford has ever launched," says Ford Focus Body Engineering Manager Graham Curle.
To compete, the car must offer improved crash-worthiness; refinement in terms of noise; vibration and harshness (NVH); and be able to comfortably accommodate drivers of all shapes and sizes. Apparently it does, having won the 1999 European Car of the Year by almost 200 points, according to O'Connor. "Focus raises the bar for small cars in terms of roominess, comfort, driving dynamics, and safety," says Curle.
Focus' platform is available as a 3- or 5-door hatchback, sedan, or wagon ,which, like the Model T, share many interchangeable parts. Front-end structure and design, as far back as the fuel tank, are common to all four body styles. Ford's multifunctional optimization (MFO) software, which incorporates I-DEAS Master Series from SDRC (Milford, OH), helped the Focus team optimize package, driving dynamics, comfort, fuel economy, and cost of ownership. MFO software allows engineers to look at NVH, weight, and safety as a complete entity rather than exercise each aspect independently with separate CAE tools.
To achieve the superior ride and handling of a fully independent rear suspension while keeping the cost down, engineers made extensive use of pressed-steel components in the rear suspension, and reduced friction and compliance in the front suspension and steering. But driving dynamics ultimately depend on a stiff structure. By applying the latest laser-welding technology to key body components, engineers designed a platform that's twice as stiff as its predecessor, and 15% stiffer than all recent class entrants.
Tailor-welded blanks. Tailored, laser-welded blanks are to Focus what vanadium steel was to the Model T. Childe Harold Wills' experimentation with the properties of vanadium steel, an alloy manufactured for the company at the direction of Henry Ford, gave the Model T great strength and durability without extra weight. The result was a lightness and durability characteristic of the Model T that was key to the vehicle's long-term success. Likewise "tailored blanks allow Focus to be much more robust for its weight," says Curle.
To achieve a stiffness of 826 kNm/rad, Focus' structure uses variable-thickness steel rather than exotic materials. Today's laser-welding technology offers the ability to join steel panels of different gauges to provide tailored blanks for stamping processes. "This gives engineers greater freedom in design by thinking in terms of larger parts and part consolidation, without weight penalties or restrictions in construction of multi-piece assemblies," says Ford Focus Chief Program Engineer Tony Pixton. In addition to weight savings, laser-welded blank technology enables fine-tuning of deformation characteristics, provides strength where it is required, and allows down gauging where it is not.
But tailored blanks aren't a carte blanche solution. Focus engineers carefully considered investment vs piece-cost efficiency, and kept targets for safety, durability, NVH, and weight in mind when determining if using a laser-welded blank for a particular part would be a plus on the bottom line. "For example," Curle says, "a certain combination of panels may offer a weight savings, or NVH improvement that would result in as good as crash performance, and have no effect on durability."
The rear side rails, for example, are traditionally made from four separate parts, according to Curle, "For Focus, these parts are replaced with a single laser-welded blank, with a three stage gauge change." Tailoring the blank prior to stamping allows the side rail to have a thinner gauge to improve weld strength near the passenger compartment. The heaviest gauge in the middle provides rigid mounting points for the suspension, and then a different gauge to optimize the rear crush structure, while simultaneously saving more than 1 kg per rail in weight. "Laser-welded blank technology allowed us to optimize in terms of weight, manufacturing assembly, and rear crash performance," says Curle. "With tailored blanks you can put the weld lines where you want them, keep them out of a plane of stress, and achieve the desired crash performance without having to add any local stiff areas."
Similarly, the gauge of steel in the B-pillar is 2.25-mm thick at the top but tapers to just 1.1 mm at the base, providing a stiff upper section for superior performance in the event of a side-impact crash. "We needed a very stiff B-pillar so that it would deploy at a certain rate," Curle explains, "but at the same time, we wanted it to pivot around the rocker so that it wouldn't buckle, bend, or collapse prematurely." A tailored blank let engineers design a small thinner gauge area at the root of the B-pillar joint that allows it to rotate, but still remain intact. Not rip the B-pillar off the rocker for example, but allow it to deform at a fixed speed and not increase in velocity. "We wouldn't have been able to get that kind of performance with conventional joining methods. Laser welding was the only way we were able to achieve this rotation at the base of the B-pillar, achieve the stiff structure, and hit the targets that we wanted," says Curle.
From a vehicle dynamics standpoint, Focus' highly rigid platform (boosted further by cross-members front and rear) has enabled engineers to fine-tune the front and rear suspension systems to deliver driving precision and ride comfort. "The goal was to give Focus a level of comfort, refinement and active safety normally associated with larger cars in a higher class, while providing handling and stability of a more sporty and reassuring nature," says Pixton.
Tailored blanks tackle tough design problems
Government legislation, environmental pressures, safety regulations and consumer dictates during the past two decades have pressured engineers to design lighter more fuel-efficient cars that produce lower emissions, and to deliver improved handling and crashworthiness. Tailored blanks are generating a great deal of interest in the automotive industry for their ability to reduce mass and cost, while improving structural integrity and material utilization. Although tailor-welded blanks were first developed to reduce waste by using collectible offal, today engineers use tailored blanks to fine-tune deformation characteristics, provide strength where it's needed, and down gauge where it's not.
Engineers typically use tailor-welded blanks made of sheet steels with different thicknesses, coatings, and properties in bodyside frames, door-inner panels, motor-compartment rails, center-pillar inner panels, and wheelhouse/shock tower panels. Numerous tailored blank applications currently are under consideration in North America and worldwide. At present, European carmakers, including Volvo, Mercedes-Benz, BMW, and Volkswagen, and Japanese carmakers, including Nissan and Toyota, use tailored blanks.
The cost to weld a tailored blank depends on the product design and welding system. In general, when looking at the welding cost for 25 mm (1.0 inch) of weld, the following are true:
Short welds cost more than long welds
Two identical parallel welds are approximately twice the cost of one weld
Heavy or coated steels are more costly than lighter or uncoated steels
Thicker gauge combinations cost more than thinner combinations
In-line welds cost slightly more than a continuous weld.
|Tailored blanks offer engineers greater freedom to design larger parts and reduce the number of components without weight penalties or restrictions in construction of multi-piece assemblies.|
Additional details...Contact Jack Noel, Auto/Steel Partnership, 2000 Town Center, Ste., 320, Southfield, MI 48075-1123; Fax: (248) 356-8511
Metal/plastic composite solves 'no-build' problem
Just 30 months before the Focus was due to launch in Europe, the manufacturer found itself in a no-build situation with respect to the Focus' front-end assembly. It was impossible to achieve the required quality with respect to gaps and flushness in the front end of the vehicle due to tolerance stack up in the multipiece, sheet-metal assembly.
During a combined workshop, Bayer Corp.'s Polymers Div. developed a solution: Replace existing sheet metal parts with one extremely accurate metal/plastic composite part that installs on the body's construction line. The part adjusts exactly to the outside fender lines in x, y, and z directions, and is square in x and y.
To achieve the necessary precision, this hybrid GOR (grill opening reinforcement), as it's called, uses mounting brackets for adjustment and is comprised of three sheet metal parts -- the upper cross-car member, the lower cross member, and the shield for the hood latch and lock cylinder. These are joined together by an injection-molded rib structure (nylon 6, 30% glass filled) to form a strong body component. Connection between the sheet metal and the plastic structure is purely mechanical, with sheet metal left partially exposed.
The new GOR assembly and accurate adjustment in body construction eliminates the accumulated tolerances of the underbody front end. "Even if the underbody is matchboxed," explains Ford Focus Chief Program Engineer Tony Pixton, "the upper body parts are accurate in gap and flushness and are square. Essential for the Focus front end's long, clearly visible gaps, the concept of positioning and fixing all front-end exterior components such as fenders, radiator grille, headlamps, bumper skin and hood to one single highly integrated part saves much money and assembly time."